1. Field of the Invention
The present invention relates to a novel bimetallic metallocene, and more particularly to a novel bimetallic metallocene with a high catalytic activity for preparing olefin polymers having a narrow MWD.
2. Description of the Prior Art
Olefin-based polymers have been used in a wide range of applications. One group of commonly used olefin-based polymers is polyolefins, that is, homopolymers or copolymers of olefins. These polyolefin plastics are typically used in such applications as blow and injection molding, extrusion coating, film and sheeting, pipe, wire and cable.
An example of polyolefin is ethylene-propylene elastomer (ethylene-propylene rubbers, EPR). It has many end-use applications due to its resistance to weather, good heat aging properties and its ability to be compounded with large quantities of fillers and plasticizers. Typical automotive uses are radiator and heater hoses, vacuum tubing, weather stripping and sponge doorseals. Typical industrial uses are sponge parts, gaskets and seals.
Another group of commonly used olefin-based polymers is terpolymers of ethylene, propylene, and a non-conjugated diene, which are generally referred to as EPDM elastomers. EPDM elastomers have outstanding weather and acid resistance, and high and low temperature performance properties. Such properties particularly suit EPDM elastomers for use in hoses, gaskets, belts, bumpers, as blending components for plastics and for tire side walls in the automotive industry, and for roofing applications. Additionally, because of their electrical insulation properties, EPDMs are particularly well suited for use as wire and cable insulation.
To date, many catalyst systems have been developed for olefin polymerization, these mainly being classified into two types: Ziegler-Natta catalyst systems and metallocene catalyst systems.
Ziegler et. al. in U.S. Pat. No. 3,113,115 uses TiCl.sub.4 /AlEtCl.sub.2 catalyst system to produce EPR. Natta et. al. in U.S. Pat. No. 3,300,459 uses VOCl.sub.3 /Al(C.sub.6 H.sub.13).sub.3 catalyst system to produce EPR.
Floyd and Hoel in U.S. Pat. Nos. 5,001,205; 4,871,705; and 5,229,478 use metallocenes such as biscyclopentadienyl compounds to produce olefin polymers. The Dow Chemical Company in WO 9,308,221 and European Patent No. 0,416,815 A2 developed monocyclopentadienyl compounds, in which the cyclopentadienyl group is substituted with a constrain-inducing moiety, such as dimethylsilyl. However, synthesis of this particular constained geometry catalyst (CGC) has a low yield (about 30%).
Davis in U.S. Pat. No. 5,372,980 use a bimetallic metallocene as a catalyst to produce olefin polymers. The catalytic activity is below 1.0.times.10.sup.5 g-polymer/g-metal-hr.